This invention relates to a color photothermographic element containing a mixture of blocked developing agents. In particular, a mixture of at least two blocked developers having different onset temperatures can be used to balance the image formed in different imaging layers during thermal development, for example imaging layers in different color units.
In conventional color photography, films containing light-sensitive silver halide are employed in hand-held cameras. Upon exposure, the film carries a latent image that is only revealed after suitable processing. These elements have historically been processed by treating the camera-exposed film with at least a developing solution having a developing agent that acts to form an image in cooperation with components in the film. Developing agents commonly used are reducing agents, for example, p-aminophenols or p-phenylenediamines.
Typically, developing agents (also herein referred to as developers) present in developer solutions are brought into reactive association with exposed photographic film elements at the time of processing. Segregation of the developer and the film element has been necessary because the incorporation of developers directly into sensitized photographic elements can lead to desensitization of the silver halide emulsion and undesirable fog. Considerable effort, however, has been directed to producing effective blocked developing agents (also referred to herein as blocked developers) that might be introduced into silver halide emulsion elements without deleterious desensitization or fog effects. Accordingly, blocked developing agents have been sought that would unblock under preselected conditions of development after which such developing agents would be free to participate in image-forming (dye or silver metal forming) reactions.
U.S. Pat. No. 3,342,599 to Reeves discloses the use of Schiff-base developer precursors. Schleigh and Faul, in a Research Disclosure (129 (1975) pp. 27-30), describes the quaternary blocking of color developers and the acetamido blocking of p-phenylenediamines. (All Research Disclosures referenced herein are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND.) Subsequently, U.S. Pat. No. 4,157,915 to Hamaoka et al. and U.S. Pat. No. 4,060,418 to Waxman and Mourning describe the preparation and use of blocked p-phenylenediamines in an image-receiving sheet for color diffusion transfer. In addition to the aforementioned U.S. Pat. No. 4,157,915, blocked developing agents involving xcex2-elimination reactions during unblocking have been disclosed in European Patent Application 393523 and kokais 57076453; 2131253; and 63123046, the latter specifically in the context of photothermographic elements.
All of these approaches have failed in practical product applications because of one or more of the following problems: desensitization of sensitized silver halide; unacceptably slow unblocking kinetics; instability of blocked developer yielding increased fog and/or decreased Dmax after storage, lack of simple methods for releasing the blocked developer, inadequate or poor image formation, and other problems. Especially in the area of photothermographic color films, other potential problems include poor discrimination and poor dye-forming activity.
Recent developments in blocking and switching chemistry have led to blocked developing agents, including p-phenylenediamines, that perform relatively well. In particular, compounds having xe2x80x9cxcex2-ketoesterxe2x80x9d type blocking groups (strictly, xcex2-ketoacyl blocking groups) are described in U.S. Pat. No. 5,019,492. With the advent of the xcex2-ketoester blocking chemistry, it has become possible to incorporate p-phenylenediamine developers in film systems in a form from which they only become active when required for development. The xcex2-ketoacyl blocked developers are released from the film layers in which they are incorporated by an alkaline developing solution containing a dinucleophile, for example hydroxylamine.
It is an object of the invention to obtain improved color photothermographic imaging elements and methods for their development employing incorporated blocked developing agents, also referred to herein as blocked developers. With respect to color photothermographic imaging elements, it is desirable to employ a blocked developer that is stable until development yet can rapidly and easily develop a high quality image once processing has been initiated by heating the element or by applying to the element a processing solution during or after heating, such as a solution of a base or acid or pure water. A completely dry process or an apparently dry process (for example, in which the volume of aqueous solutions is small enough to be applied by a laminate) is most desirable and, in fact, the eliminating the application of all or most solutions and photochemical processing chemicals is one of the main advantages of a dry or apparently dry photothermographic system. The existence of such a process would allow for very rapidly processed films that can be processed simply and efficiently in photoprocessing kiosks. Such kiosks, with increased numbers and accessibility, could ultimately allow for, relatively speaking, anytime and anywhere silver-halide film development.
One of the factors to be considered, with respect to a blocked developer in a color photothermographic element, is the onset temperature of the blocked developer, that is, the temperature at which the compound becomes substantially unblocked or activated, which is generally a measure or indication of the temperature at which the development process will need to be performed. In generally, other factors being equal, the higher the onset temperature, the higher the process temperature. A process at lower temperatures generally has less side reactions and is less expensive to accomplish. There is less potential deformation of the film base which can adversely affect image quality. Also, higher temperatures tend to undesirably decompose components in the photographic element and release volatile vapors.
Another factor to be considered, with respect to a blocked developer in a photothermographic element, is the discrimination of the image, generally defined as the difference of between Dmin and Dmax at the process temperature. Since the discrimination of an image, using a blocked developer, will generally vary with process temperature, it is usually desirable to process the film at the temperature of peak discrimination (in the photographic element). It is further desirable that the film have a high peak discrimination. Discrimination of a film can be affected by a number of factors, including photographic emulsion type and finish, the kind and amount of couple, the thermal solvent, and other factors. However, a key factor is the blocked developing agent incorporated in the photothermographic film.
A problem with a blocked developer is that discrimination may be poor if the blocked developer unblocks to quickly or does not unblock quickly enough. It is advantageous to appropriately balance the reactivity of the developing agent, during developing, with the rate of release of the developing agent from the blocked developing agent. If the reactivity of developing agent with the coupling agent (or xe2x80x9ccouplerxe2x80x9d) to form the image dye is too much less than the rate of release of the developing agent, at a particular temperature, then there is the opportunity for side reactions to occur which may decrease the discrimination. (usually by increasing fog) and consequently decrease image quality. On the other hand, if the reactivity of the developing agent with the coupling agent is too much greater than the rate of release of the developing agent, at the temperature of development, then there may not be enough developing agent for image formation to occur which may also decrease discrimination (this time, usually by decreasing Dmax) which again will consequently decrease image quality.
Another problem with blocked developers is that, if the relative discrimination curve (a graph of peak discrimination versus temperature of processing) is too narrow, then the release of the blocked developer in the photographic element as the temperature of the element increases may not be well timed. This may result, for example, in only a small portion of the blocked developer being unblocked as the photographic element is being heated and then, as the element nears the equilibrium temperature, a large amount of blocked developer being unblocked all at once, drowning the coupler with an excess of developing agent, resulting in poor discrimination (high Dmin). It is to be understood that, even though a heater may reach its equilibrium temperature quickly, the photographic element may take some process time to reach its equilibrium or peak temperature, which optionally may be set higher than the temperature of peak discrimination in order to speed the development process.
In general, a broader and flatter relative discrimination curve is desirable. Not only is it more robust relative to variations in process conditions, but it can provide a relatively steady release or unblocking of the developing agent so that the release of the developing agent better matches the reactivity of the developing agent with the coupler and its concentration. This can increase the amount of development occurring at a temperature in the vicinity of peak discrimination for the process. In other words, there is a broader temperature area (element temperature) over which peak discrimination, or near peak discrimination, occurs.
Thus, it would be desirable if a higher percentage of peak discrimination for the photothermographic element occurs within over a given temperature range around the peak discrimination temperature, wherein peak discrimination temperature is defined as the temperature at which discrimination peaks when heating the photographic element.
If the relative discrimination curve is narrow, then the photographic element may reach its peak discrimination temperature very quickly without having had time to release the developing agent and then may release the developing agent all at once, which would result, as mentioned above, in the flooding the couplers and poor discrimination. Although one might compensate by heating slower, it is desirable to heat the photographic element quickly to avoid adverse affects of prolonged heating on the photographic element. Thus, it is better to have flatter curve, to provide maximum discrimination for the time period and temperature range of the photothermographic element during the heating process.
It is also desirable to balance the discrimination between layers, particularly between or among color units, of which there are typically three in a color film. A problem with color film has been the fact that the discrimination in different color layers can vary considerably, more so than in conventional film. A blocked developing agent may have the correct reactivity in one color layer, but may have too much reactivity or too little reactivity in another color layer.
An individual blocked developer can react with distinct couplers to form dyes of distinct hues. A problem arises when a single blocked developer is employed to form distinct dye deposits of different hue in distinct color record layer units of a film since the distinct couplers can react with the released developer at distinct rates and form dye deposits differing in gamma, speed and density. These differences in turn lead to color records that are practically imbalanced and can be difficult to scan.
Distinct blocked developers are employed in one or more of the color records to solve this problem. The blocked developer can be matched with the couplers employed in distinct color records to provide dye records of a desired hue and stability, and simultaneously having desired gamma, latitude and density characteristics suitable for scanning. In this context, the hue and stability of a chromogenic dye deposit in a specific layer is controlled by the identity of the coupler, the identity of the developer and the presence and level of any coupler solvent or melt former. The gamma, latitude, and density however can be controlled by choice of the moiety chosen to block the active sites of a developer and by the identity and level of any present melt former.
For example, a film can be prepared having three color forming layer units respectively sensitive to blue, green and red light. A distinct coupler chosen to provide a dye of distinct hue and stability and suitable for scanning when that coupler reacts with a specific developer is associated with each color unit. A blocked developer is placed in reactive association with each color unit. The blocking moiety of each blocked developer is chosen to enable release of the developer at a rate suitable for the formation of a dye deposit having desired latitude, density, fog and gamma characteristics. The developer moiety of the blocked developer for each layer unit is chosen to provide a dye of desired hue and stability. Thus, film structures having a desired dye hue, dye stability, latitude, density, fog and gamma are prepared. It is possible for a common developing agent to be employed in the blocked developers in the aforesaid mentioned color film but with distinct blocking moieties. It is also possible to employ a common blocking moiety in the blocked developers in the aforesaid mentioned color film but with distinct developing agents. It is also possible to incorporate a melt formers or other addenda which can be selected to modulate the hue, density, reactivity, speed, gamma, fog and stability characteristics of the formed dye deposits.
Nevertheless, it is extremely difficult to develop separate blocked developers for different imaging layers in which the layers are well balanced.
It is an object of this invention, and it would be highly desirable, to obtain a color photothermographic element in which the density and color is well balanced between different imaging layers, especially in different color units.
The term xe2x80x9conset temperaturexe2x80x9d or To is defined as the temperature required to produce a maximum density (Dmax) of 0.5, as described in the Examples below. Lower temperatures indicate more active developers which are desirable.
The term xe2x80x9cprocess temperaturexe2x80x9d is defined herein as the maximum temperature present in the photographic element during the development process, which may approximate the maximum temperature of the environment with which the photographic element is directly contacted during the development process, which in turn can approximate the temperature of the heating element (source of heat) during the development process in cases of good heat transfer.
The term xe2x80x9cdiscriminationxe2x80x9d herein generally means the difference between Dmax and Dmin in an imaging layer.
The term xe2x80x9cpeak discriminationxe2x80x9d or DP is defined, as in the Examples, for the optimum platen temperature, as corresponding to the value of the difference between Dmax and Dmin (Dmaxxe2x88x92Dmin) divided by Dmin.
The term xe2x80x9crelative discrimination curvexe2x80x9d herein means the discrimination as the temperature of the blocked developer varies.
The term xe2x80x9cpeak discrimination temperaturexe2x80x9d herein means the maximum discrimination in the relative discrimination curve.
The term xe2x80x9cExe2x80x9d means herein the exposure in lux-seconds.
The term xe2x80x9cgamma ratioxe2x80x99 when applied to a color recording layer unit refers to the ratio determined by dividing the color gamma of a cited layer unit after an imagewise color separation exposure and process that enables development of primarily that layer unit by the color gamma of the same layer unit after imagewise white light exposure and process that enables development of all layer units. In turn, the term xe2x80x9cgammaxe2x80x9d is employed to indicate the incremental increase in image density (xcex94D)produced by a corresponding incremental increase in log exposure (xcex94log E)and indicates the maximum gamma measured over an exposure range extending between a first characteristic curve reference point lying at a density of 0.15 above minimum density and a second characteristic curve reference point separated from the first reference point by 0.9 log E.
The term xe2x80x9ccouplerxe2x80x9d indicates a compound that reacts with oxidized color developing agent to create or modify the hue of a dye chromophore.
In referring to blue, green and red recording dye image-forming layer units, the term xe2x80x9clayer unitxe2x80x9d indicates the hydrophilic colloid layer or layers that contain radiation-sensitive silver halide grains to capture exposing radiation and couplers that react upon development of the grains. The grains and couplers are usually in the same layer, but can be in adjacent layers.
The term xe2x80x9cdye image-forming couplerxe2x80x9d indicates a coupler that reacts with oxidized color developing agent to produce a dye image.
Research Disclosure is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North St., Emsworth, Hampshire P010 7DQ, England.
The term xe2x80x9cone-time-use cameraxe2x80x9d or xe2x80x9cOTUCxe2x80x9d is used to indicate a camera supplied to the user preloaded with a light sensitive silver halide photographic element and having a lens and shutter. The terms xe2x80x9csingle-use camera,xe2x80x9d xe2x80x9cfilm-with-lens unit,xe2x80x9d xe2x80x9cdisposable cameraxe2x80x9d and the like are also employed in the art for cameras that are intended for one use, after which they are recycled, subsequent to removal of the film for development.
The term xe2x80x9cexposure latitudexe2x80x9d indicates the exposure range of a characteristic curve segment over which instantaneous gamma (xcex94D/xcex94log E) is at least 25 percent of gamma, as defined above. The exposure latitude of a color element having multiple color recording units is the exposure range over which the characteristic curves of the red, green, and blue color recording units simultaneously fulfill the aforesaid definition.
The term xe2x80x9cabsorption half-peak bandwidthxe2x80x9d indicates the spectral range over which a dye exhibits an absorption equal to at least half of its peak absorption.
By having different blocked developers or mixtures of at least two blocked developers in different color layers, it is possible to manipulate, the image discrimination (at the processing temperature) in each layer and to balance the density formation or color in the different color layers. Different mixtures of blocked developers can be used in different imaging layers, to balance the density formation in distinct color records.
Accordingly, at least one Blocked Developer C is used in a first imaging layer (Layer 1) and a mixture of at least two blocked developers, Blocked Developers A and B is used in a second imaging layer (Layer 2). Preferably, Layer 1 and 2 are in different color units, although they may be in the same color unit.
According to one embodiment of the invention, the Gamma Ratio (at the process temperature) of the Gamma in Layer 1 or Color Unit 1 to the Gamma in Layer 2 or Color Unit 2 is between 0.8 and 1.2, preferably 0.9 and 1.1, and wherein this Gamma Ratio is at least 10% closer to 1.0 than if only one of Blocked Developers A, B, and C are independently used in each of Layer/Color Unit 1 and Layer/Color Unit 2.
According to a second embodiment of the invention, the Dmin Ratio (at the process temperature) of the Dmin in Layer 1 or Color Unit 1 to the Dmin in Layer 2 or Color Unit 2 is between 0.8 and 1.2, preferably 0.9 and 1.1, and wherein this Dmin ratio is at least 10% closer to 1.0 than if only one of Blocked Developers A, B, and C are independently used in each of Layer/Color Unit 1 and Layer/Color Unit 2.
According to a third embodiment of the invention, the Latitude Ratio (at the process temperature) of the Latitude in Layer 1 or Color Unit 1 to the Latitude in Layer 2 or Color Unit 2 is between 0.8 and 1.2, preferably 0.9 and 1.1, and wherein this Latitude Ratio is at least 10% closer to 1.0 than if only one of Blocked Developers A, B, and C are independently used in each of Layer/Color Unit 1 or Layer/Color Unit 2.
Thus, this invention relates to a photothermographic color element containing a mixture of at least two different blocked developers in the same emulsion layer, which blocked developers having different onset temperatures.
By different blocked developers is meant two blocked developing agents having (1) the same developing agent upon unblocking, but having different blocking/timing groups, (2) the same blocking and/or timing groups but different developing agents when unblocked, and/or (3) both different developing agents upon complete unblocking and different blocking and/or timing groups.
Thus, the present invention can be used as a film-building tool. A different blocked developer in one layer can be used to increase the reactivity of a layer relative to another and consequently allow more development in a layer as needed and/or a different blocking moiety on the developing agent (including blocking and timing groups) may be used so that more developing agent can be released at a certain process temperature. The concentration of developing agent and the concentration of the coupler can be balanced to get comparable amounts of dye in each layer of color unit. When the extinction of dye lower in a layer or color unit, then more developing agent may be used to get a comparable amount of density. Thus, the present invention can be used to balance the sensitometric curve. A range of adjustments in the sensitometry in different layers can be made by using mixtures of blocked developers and by varying the proportion of the blocked developers in the mixture.
The term blocking/timing group is meant the portion of the blocked developer other than the developing agent that reacts with a coupler. The blocking/timing group, therefore, separates from the developing agent, even if in stages, over time.
In one embodiment of the invention, mixtures of blocked developers have been found that provide lower processing temperatures and/or shorter times of development compared to the blocked developer alone having the higher onset temperature, and at the same time, improved discrimination compared to the blocked developer alone having the lower onset temperature. In some cases, higher peak discrimination than obtainable with either of the blocked developers alone at the given process temperature is obtainable.
In another embodiment of the invention, mixtures of blocked developers have been found that provide a lower gamma of the relative discrimination curve at the processing temperature, thereby providing a generally flatter and more robust relative discrimination curve compared to either blocked developer alone.
Preferably, when the developer mixture is used in a dry physical development system, the developer is thermally activated at temperatures between about 80 and 180xc2x0 C., preferably 100 to 170xc2x0 C. When the developer is used in an apparently dry chemical development system, however, the developer mixture is preferably thermally activated at temperatures between about 60 and 120xc2x0 C., preferable 65 to 100xc2x0 C., in the presence of added acid, base or water.
In particular, the present invention is directed to a color photothermographic color element comprising at least three light-sensitive units that have their individual sensitivities in different wavelength regions comprising a silver halide imaging layer having associated therewith a mixture of at least two blocked developing agents comprising a Blocked Developer A and blocked Developer B independently represented by Structure I:
DEVxe2x80x94(LINK 1)lxe2x80x94(TIME)mxe2x80x94(LINK 2)nxe2x80x94M
wherein,
DEV is a silver-halide color developing agent;
LINK 1 and LINK 2 are linking groups;
TIME is a timing group;
l is 0 or 1;
m is 0, 1, or 2;
n is 0 or 4;
l+n is 1 or 2;
M is a blocking group or M is:
xe2x80x94Mxe2x80x2xe2x80x94(LINK 2)nxe2x80x94(TIME)mxe2x80x94(LINK 1)lDEV
wherein Mxe2x80x2 is a blocking group that also contains another blocked developer, which may be the same or a different developing agents; and
wherein the onset temperature of Blocked Developer A is less than the onset temperature of Blocked Developer B, the onset temperature of Blocked Developer A is in the range of 110C. to 160C., preferably 110 to 150, and the onset temperature of Blocked Developer B is in the range of 130 to 170C., preferably 140 to 160C., and the difference in the onset temperatures of the two Blocked Developers is 5 to 50C., preferably 8 to 40, more preferably 10 to 30C.
In a preferred embodiment of the invention, the peak discrimination of the mixture of Blocked Developer A and Blocked Developer B will be higher that the discrimination of Blocked Developer B. In a particularly preferred embodiment, the peak discrimination of the mixture is higher than the peak discrimination of both Blocked Developer A and Blocked Developer B.
The invention additionally relates to a method of image formation having the steps of: thermally developing an imagewise exposed photographic element having a mixture of blocked developers as described above that decomposes to release corresponding developing agents on thermal activation to form a developed image. Preferably, following development, the developed image is then scanned to form a first electronic-image representation (or xe2x80x9celectronic recordxe2x80x9d) from said developed image, the first electronic record is digitized to form a digital image, and the digital image is modified to form a second electronic-image representation, which can be stored, transmitted, printed or displayed.
The invention further relates to a one-time use camera having a light sensitive photographic element comprising a support and a mixture of blocked developers as described above that releases a mixture of developing agents or differentially releases the same developing agents (in the same or different imaging layers) on thermal activation. The invention further relates to a method of image formation having the steps of imagewise exposing such a light sensitive photographic element on thermal activation in a one-time-use camera having a heater and thermally processing the exposed element in the camera.
In a preferred embodiment of the invention, LINK 1 and LINK 2 are of structure II: 
wherein
X represents carbon or sulfur;
Y represents oxygen, sulfur or Nxe2x80x94R1, where R1 is substituted or unsubstituted alkyl or substituted or unsubstituted aryl;
p is 1 or 2;
Z represents carbon, oxygen or sulfur;
r is 0 or 1;
with the proviso that when X is carbon, both p and r are 1, when X is sulfur, Y is oxygen, p is 2 and r is 0;
# denotes the bond to PUG (for LINK 1) or TIME (for LINK 2):
$ denotes the bond to TIME (for LINK 1) or T(t) substituted carbon (for LINK 2).